Cyanoethylated polyvinyl spacer layers for image-receiving element



Dec. 31, 1968 H. c. HAAS ET AL 3,419,389

CYANOETHYLATED POLYVINYL SPACER LAYERS FOR IMAGE-RECEIVING ELEMENT Filed May 26. 1967 Sheet of 2 OLYMERIC ACID LAYER SUPPORT LAYER TIME IN SECONDS (ALKALI PERMEABILITY) FIGE IBO- I80- v POLYVINYL ALCOHOL 56% CYANOETHYLATED POLYVINYL ALCOHOL.

m- I20- 82 I20- UJUJ F i G. 2 2Q F I G. 3 90- u 90 5 .3 MILS 1 so 020 MILS v OIO MILS o T E o so so 70 so 90 I00 so I00 TEMPERATURE F TEMPERATURE F INgENTORS amd BY ill/My aim 3250mm w mama, awn W 420mm ATTORNEYS Dec. 31, 1968 H. c. HAAS ET AL CYANOETHYLATED POLYVINYL SPACER LAYERS FOR IMAGE-RECEIVING ELEMENT Sheet Filed May 26. 1967 m m TL A u 0 8 mm 4 L E M M mm mu G s m N I: 7 R W 2 .0 Am F. M 0 90 s E 5P H.- WT M M o l 5 0 mu mu 0 O 5 Q 9 6 w INVENTORS M6. Idem W dflolwimki 7511014401, a! m Am: mm

ATTORNEYS Y B O D F m 1. n F Y Hm 9 T L s E m n m NL M 8T A 5 R Cm 2 OE V O 7P %w G M 20 I E 6? .O F s .0 .5 J a 0 m w m w e United States Patent 3,419,339 CYANOETHYLATED POLYVINYL SPACER LAY- ERS FOR IMAGE-RECEIVING ELEMENT Howard C. Haas, Arlington, and Henry S. Kolesinski, Burlington, Mass., assignors to Polaroid Corporation,

Cambridge, Mass., a corporation of Delaware Filed May 26, 1967, Ser. No. 641,657 12 Claims. (Cl. 963) The present invention relates to photography and, more particularly, to processes for forming photographic diffusion transfer color images and products particularly adapted for employment in such processes.

In processes of the type set forth in U.S. Patent No. 2,983,606, a photosensitive element containing a dye developer and a silver halide emulsion is exposed and wetted by a liquid processing composition, for example, by immersion, coating, spraying, flowing, etc., in the dark, and the exposed photosensitive element is superposed prior to, during, or after wetting, on a sheetlike support element which may be utilized as an image-receiving element. In a preferred embodiment, the liquid processing composition is applied to the photosensitive element in a substantially uniform layer as the photosensitive element is brought into superposed relationship with the image-receiving layer. The liquid processing composition permeates the emulsion to initiate development of the latent image contained therein. The dye developer is immobilized or precipitated in exposed areas as a consequence of the development of the latent image. This immobilization is apparently, at least in part, due to a change in the solubility characteristics of the dye developer upon oxidation and especially as regards its solubility in alkaline solutions. It may also be due in part to a tanning effect on the emulsion by oxidized developing agent, and in part to a localized exhaustion of alkali as a result of development. In unexposed and partially exposed areas of the emulsion, the dye developer is unreacted and diffusible and thus provides an imagewise distribution of unoxidized dye developer dissolved in the liquid processing composition as a function of the pointto-point degree of exposure of the silver halide emulsion. At least part of this imagewise distribution of unoxidized dye developer is transferred, by imbibition, to a superposed image-receiving layer or element, said transfer substantially excluding oxidized dye developer. The imagereceiving element receives a depthwise diffusion from the developed emulsion of unoxidized dye developer without appreciably disturbing the imagewise distribution thereof to provide the reversed or positive color image of the developed image. The desired positive image is revealed by stripping the image-receiving layer from the photosensitive element at the end of a suitable imbibition period.

The dye developers, as noted above, are compounds which contain in the same molecule both the chromophoric system of a dye and also a silver halide developing function. By a silver halide developing function is meant a grouping adapted to develop expose-d silver halide. A preferred silver halide development function is a hydroquinonyl group. Other suitable developing functions include ortho-dihydroxyphenyl and orthoand para-amino substituted hydroxyphenyl groups. In general, the development function includes a benzenoid developing function, that is, an aromatic developing group which forms quinonoid or quinone substances when oxidized.

Multicolor images may be obtained using color imageforming components such as, for example, the previously mentioned dye developers, in diffusion transfer processes. One technique contemplates the use of a photoice sensitive silver halide stratum comprising at least two sets of selectively sensitized minute photosensitive elc ments arranged in the form of a photosensitive screen. Transfer processes of this type are disclosed in U.S. Patents Nos. 2,968,554 and 2,983,606. In such an embodiment, each of the minute photosensitive elements has associated therewith an appropriate dye developer in or behind the silver halide emulsion portion. In general, a suitable photosensitive screen, prepared in accordance with the disclosures of said patents, comprises minute red-sensitized emulsion elements, minute green-sensitized emulsion elements and minute blue-sensitized emulsion elements arranged in side-by-side relationship in a screen pattern and having associated therewith, respectively, a cyan dye developer, a magenta dye developer and a yellow dye developer.

Another process for obtaining multicolor transfer images utilizing dye developers employs an integral multilayer photosensitive element, such as is disclosed in copending U.S. application Ser. No. 565,135, filed on Feb. 13, 1956, and now U.S. Patent 3,345,135, wherein at least two selectively sensitized photosensitive strata are superposed on a single support and are processed, simultaneously and without separation, with a single, common image-receiving layer. A suitable arrangement of this type comprises a support carrying a red-sensitive silver halide emulsion stratum, a green-sensitive silver halide emulsion stratum and a blue-sensitive silver halide emulsion stratum, said emulsions having associated therewith, respectively, for example, a cyan dye developer, a magenta dye developer and a yellow dye developer. The dye developer may be utilized in the silver halide emulsion layer, for example, in the form of particles, or it may be employed as a layer behind the appropriate silver halide emulsion strata. Each set of silver halide emulsion and associated dye developer strata may be separated from other sets by suitable interlayers, for example, by a layer of gelatin or polyvinyl alcohol. In certain instances, it may be desirable to incorporate a yellow filter in front of the green-sensitive emulsion and such yellow filter may be incorporated in an interlayer. However, where desirable, a yellow dye developer of the appropriate spectral characteristics and present in a state capable of functioning as a yellow filter may be employed. In such instances, a separate yellow filter may be omitted.

Copending U.S. application Ser. No. 234,864, filed Nov. 1, 1962, now U.S. Patent 3,362,819, discloses image-receiving elements particularly adapted for employment in the preceding diffusion transfer processes which elements comprise a support layer possessing on one surface thereof, in sequence, a polymeric acid layer; an inert timing or spacer layer; and an image-receiving layer adapted to provide a visible image upon transfer to said layer of diffusible dye image-forming substances.

As set forth in the last-mentioned application, the polymeric acid layer comprises polymers which contain acid groups, such as carboxylic acid and sulfonic acid groups, which are capable of forming salts with alkali metals, such as sodium, potassium, etc., or with organic bases, particularly quaternary ammonium bases, such as tetramethyl ammonium hydroxide, or potentially acidyielding groups, such as anhydrides or lactones, or other groups which are capable of reacting with bases to capture and retain them. The acid-reacting group is, of course, nondiffusible from the acid polymer layer. In the preferred embodiments disclosed, the acid polymer contains free carboxyl groups and the transfer processing composition employed contains a large concentration of sodium and/ or potassium ions. The acid polymers stated to be most useful are characterized by containing free carboxyl groups,

being insoluble in water in the free acid form, and by forming water-soluble sodium and/ or potassium salts. One may also employ polymers containing carboxylic acid anhydride groups, at least some of which preferably have been converted to free carboxyl groups prior to imbibition. While the most readily available polymeric acids are derivatives of cellulose or of vinyl polymers, polymeric acids from other classes of polymers may be used. As examples of specific polymeric acids set forth in the application, mention may be made of dibasic acid half-ester derivatives of cellulose which derivatives contain free carboxyl groups, e.g., cellulose acetate hydrogen phthalate, cellulose acetate hydrogen glutarate, cellulose acetate hydrogen succinate, ethyl cellulose hydrogen succinate, ethyl cellulose acetate hydrogen succinate, cellulose acetate hydrogen succinate hydrogen phthalate; ether and ester derivatives of cellulose modified with sulfoanhydrides, e.g., with ortho-sulfobenzoic anhydride; polystyrene sulfonic acid; carboxymethyl cellulose; polyvinyl hydrogen phthalate; polyvinyl acetate hydrogen phthalate; polyacrylic acid; acetals of polyvinyl alcohol with carboxy or sulfo substituted aldehydes, e.g., m-, or p-benzaldehyde stilfonic acid or carboxylic acid; partial esters of ethylene/ maleic anhydride copolymers; partial esters of methylvinyl ether/maleic anhydride copolymers; etc.

The acid polymer layer is disclosed to contain at least sufficient acid groups to effect a reduction in the pH of the image layer from a pH of about 13 to 14 to a pH of at least 11 or lower at the end of the imbibition period, and preferably to a pH of about 5 to 8 within a short time after imbibition. As previously noted, the pH of the processing composition preferably is of the order of at least 13 to 14.

It is, of course, necessary that the action of the polymeric acid be so controlled as not to interfere with either development of the negative or image transfer of unoxidized dye developers. For this reason, the pH of the image layer is kept at a level of pH 12 to 14 until the positive dye image has been formed after which the pH is reduced very rapidly to at least about pH 11, and preferably about pH 9 to 10, before the positive transfer image is separated and exposed to air. Unoxidized dye developers containing hydroquinonyl developing radicals diffuse from the negative to the positive as the quaternary ammonium, sodium or other alkali salt. The diffusion rate of such dye imageforming components is at least partly a function of the alkali concentration, and it is necessary that the pH of the image layer remain on the order of 12 to 14 until transfer of the necessary quantity of dye has been accomplished. The subsequent pH reduction, in addition to its desirable effect upon image light stability, serves a highly valuable photographic function by substantially terminating further rye transfer. The processing technique thus effectively minimizes changes in color balance as a result of longer imbibition times in multicolor transfer processes using multilayer negatives.

In order to prevent premature pH reduction during transfer processing, as evidenced, for example, by an undesired reduction in positive image density, the acid groups are disclosed to be so disturbed in the acid polymer layer that the rate of their availability to the alkali is controllable, e.g., as a function of the rate of swelling of the polymer layer which rate in turn has a direct relationship to the diffusion rate of the hydroxyl ions. The desired distribution of the acid groups in the acid polymer layer may be effected by mixing the acid polymer with a polymer free of acid groups, or lower in concentration of acid groups, and compatible therewith, or by using only the acid polymer but selecting one having a relatively lower proportion of acid groups. These embodiments are illustrated, respectively, in the above-mentioned copending application, Ser. No. 234,864 by (a) a mixture of cellulose acetate and cellulose acetate hydrogen phthalate and (b) a cellulose acetate hydrogen phthalate polymer having a much lower percentage of phthalyl groups than the first-mentioned cellulose acetate hydrogen phthalate.

It is also disclosed that the layer containing the polymeric acid may contain a water insoluble polymer, preferably a cellulose ester, which acts to control or modulate the rate at which the alkali salt of the polymer acid is formed. As examples of cellulose esters contemplated for use, mention is made of cellulose acetate, cellulose acetate butyrate, etc. The particular polymers and combinations of polymers employed in any given embodiment are, of course, selected so as to have adequate wet and dry strength and when necessary or desirable, suitable subcoats may be employed to help the various polymeric layers adhere to each other during storage and use.

The inert spacer layer of the aforementioned copending application, for example, a layer comprising polyvinyl alcohol or gelatin, acts to time control the pH reduction by the polymeric acid layer. This timing is disclosed to be a function of the rate at which the alkali diffuses through the inert spacer layer. It was stated to have been found that the pH does not drop until the alkali has passed through the spacer layer, i.e., the pH is not reduced to any significant extent by the mere diffusion into the spacer layer, but the pH drops quite rapidly once the alkali diffuses through the spacer layer into the acid polymer layer.

As examples of materials for use as the image-receiving layer, mention may be made of solution dyeable polymers such as nylons, as, for example, N-methoxymethyl polyhexamethylene adipamide; partially hydrolyzed polyvinyl acetate; polyvinyl alcohol with or without plasticizers; cellulose acetate with fillers as, for example, onehalf cellulose acetate and one-half oleic acid; gelatin; and other materials of a similar nature. Preferred materials comprise polyvinyl alcohol or gelatin containing a dye mordant such as poly-4-vinylpyridine, as disclosed in US. Patent No. 3,148,061, issued Sept. 8, 1964.

It is a primary object of the present invention to provide novel photographic diffusion transfer color processes; and novel image-receiving elements particularly adapted for employment in such processes.

Another object of the present invention is to provide photographic diffusion transfer color processes exhibiting increased processing temperature latitude; and novel image-receiving elements particularly adapted to accomplish same.

A further object of the present invention is to provide novel photographic diffusion transfer color processes exhibiting constant transfer-image color characteristics over an extended temperature range; and novel image-receiving elements particularly adapted to accomplish same.

A further object of the present invention is to provide photographic diffusion transfer color processes wherein the hydrogen ion concentration during transfer processing is maintained substantially constant over an extended temperature range; and novel image-receiving elements particularly adapted to accomplish same.

A still further object of the present invention is to provide novel photographic diffusion transfer color processes wherein the hydrogen ion concentration during transfer processing is maintained substantially constant for a predetermined time interval, irrespective of the temperaturedependent diffusion rate of the alkaline processing composition utilized; and novel image-receiving elements particularly adapted to accomplish same.

A still further object of the present invention is to provide novel image-receiving elements, particularly adapted for employment in photographic diffusion transfer color processes, which comprise composite structures which include cyanoethylated polyvinyl alcohol; and novel transfer processes employing same.

A still further object of the present invention is to provide a novel image-receiving element particularly adapted for employment in photographic diffusion transfer color processes, which comprises a flexible composite structure which includes, in sequence, a support layer; a first polymeric acid layer; a second alkali solution permeable polymeric layer having specified permeability characteristics wherein said second polymeric layer comprises cyanoethylated polyvinyl alcohol; and a third solution-dyeable polymeric layer; and novel transfer processes particularly adapted to employ same.

A still further object of the present invention is to provide image-receiving elements particularly adapted for employment in photographic diffusion transfer color processes, which elements include a plurality of layers comprising, in sequence, a support layer; a first polymeric alkali metal ion acceptor layer; a second alkali metal ion temperature inversely permeable polymeric layer comprising cyanoethylated polyvinyl alcohol; and a third polymeric layer adapted to be dyed from an alkaline solution; and novel transfer processes particularly adapted to employ same.

Other objects of the present invention will in part be obvious and will in part appear hereinafter.

The invention accordingly comprises the processes involving the several steps and the relation and order of one or more of such steps with respect to each of the others, and the product possessing the features, properties and the relation of elements which are exemplified in the following detailed disclosure, and the scope of the application of which will be indicated in the claims.

For a fuller understanding of the nature and objects of the invention reference should be had to the following detailed description taken in connection with the accompanying drawings wherein:

FIGURE 1 is a cross-sectional diagrammatic representation of a receiving sheet for use in a diffusion transfer photographic process wherein a polymeric acid layer is superposed upon a support, a spacer layer comprising a polymeric material having predetermined temperaturepermeability characteristics is superposed over said polymeric acid layer, and a polymeric, dyeable layer is superposed over said spacer layer.

FIG. 2 is a graphical representation of the temperaturealkali permeability characteristics of polyvinyl alcohol films of various thicknesses when contacted with the processing composition of Example 1, below.

FIG. 3 is a graphical representation of the temperaturealkali permeability characteristics of a 0.3 mil film of 56% cyanoethylated polyvinyl alcohol when contacted with the processing composition of Example 1, below.

FIG. 4 is a graphical representation of the temperature-alkali permeability characteristics of films of 59% cyanoethylated polyvinyl alcohol at various thicknesses when contacted with the processing composition of Example 1, below.

FIG. 5 is a graphical representation of the temperature-alkali permeability characteristics of a 0.2 mil film of 62% cyanoethylated polyvinyl alcohol when contacted with the processing composition of Example 1, below.

US. Patents Nos. 2,647,049, issued July 28, 1953; 2,661,293, issued Dec. 1, 1953; 2,698,244, issued Dec. 28, 1954; 2,698,798, issued Jan. 4, 1955; and 2,802,735, issued Aug. 13, 1957, disclose substractive color diffusion transfer processes wherein color coupling techniques are utilized, which techniques comprise, at least in part, reacting one or more developing agents and one or more color formers to provide a positive color image on a superposed image-receiving layer. US. Patent No. 3,019,124, issued Jan. 30, 1962, discloses the manufacture of photographic color screen elements; and US. Patents Nos. 2,968,554, issued Jan. 17, 1961, and 2,983,606, issued May 9, 1961, disclose diffusion transfer processes wherein a color screen element is utilized to provide a multicolor positive image to a superposed image-receiving layer. US. Patent No. 2,774,668, issued Dec. 18, 1956, the copending US. application of Edwin H. Land and Howard G. Rogers, Ser. No. 565,135, filed Feb. 13, 1956, and the previously cited US. Patent No. 2,983,606 disclose diffusion transfer processes wherein dyes are utilized to provide a positive color image into a superposed imagereceiving layer.

The objects of the present invention, detailed hereinbefore, are accomplished by employment in photographic diffusion transfer color processes of the preceding general type of a novel image-receiving element which comprises a plurality of essential layers including, in sequence, a support layer; a polymeric acid layer; a permeable, polymeric spacer layer which acts as a mechanism to compensate for temperature changes in the system; and a permeable, solution-dyeable polymeric layer.

Specifically, the image-receiving element preferably comprises a flexible composite structure including a plurality of polymeric layers which comprise, in sequence, a support layer; a polymeric alkali ion acceptor layer, for example, an alkali metal or quaternary ammonium ion acceptor layer; polymeric layer having predetermined temperature-permeability characteristics; and a polymeric layer dyeable from contact with a dye-containing alkaline solution.

As disclosed in the aforementioned copending application Ser. No. 234,864, the presence of an insert spacer layer was found to be effective in evening out the various reaction rates over a wide range of temperatures, for example, by preventing premature pH reduction when imbibition is effected at temperatures above room temperature, for example, at to F. By providing an inert spacer layer, that application discloses that the rate at which alkali is available for capture in the polymeric acid layer becomes a function of the alkali diffusion rates.

It has been disclosed in copending US. application Ser. No. 447,100, filed on Apr. 9, 1965 now abandoned, that the diffusion rate of an alkali processing composition through a permeable inert polymeric spacer layer increases with increased processing temperature to the extent, for example, that at relatively high transfer processing temperatures, that is, transfer processing temperatures above approximately 80 F., a permeature decrease in the pH of the transfer processing composition occurs due, at least in part, to the rapid diffusion of alkali from the dye transfer environment and its subsequent neutralization upon contact with the polymeric acid layer. This was disclosed to be especially true of alkali traversing an inert spacer layer possessing optimum alkali-permeability characteristics within the temperature range of optimum transfer processing. Conversely, at temperatures below the optimum transfer processing range, for example, temperatures below approximately 50 F the last-mentioned inert spacer layer was found to provide an effective diffusion barrier timewise preventing effective traverse of the inert spacer layer by alkali having temperature depressed diffusion rates. This barrier resulted in maintenance of the transfer processing environments high pH for such an extended time interval as to facilitate formation of transfer image stain and its resultant degradation of the positive transfer images color definition.

It was further disclosed in the last-mentioned application, that if the inert spacer layer of the print-receiving element is replaced by a spacer layer which comprises a permeable polymeric layer exhibiting permeability inversely dependent upon temperature, and specifically a polymeric film-forming material which exhibits decreasing permeability to solubilized alkali derived cations such as alkali metal and quaternary ammonium ions under conditions of increasing temperature, that the positive transfer image defects resultant from the aforementioned overextended pH maintenance and/or premature pH reduction were obviated.

As examples of polymers disclosed in the last-mentioned application which exhibit inverse temperature-dependent permeability to alkali, mention was made of: hydroxypropyl polyvinyl alcohol, polyvinyl methyl ether, polyethylene oxide, polyvinyl oxazolidinone, hydroxypropyl methyl cellulose, partial acetals of polyvinyl alcohol such as partial polyvinyl butyral, partial polyvinyl formal, partial polyvinyl acetal, partial polyvinyl propional, and the like.

Specifically, the spacer layer of the last-described printreceiving element comprises a permeable polymeric layer exhibiting, in a photographic diffusion transfer environment, a photographic processing-composition permeability inversely dependent on processing temperature, when compared with, or measured against, polymers disclosed in the art for the identified photo-graphic use. In general, such polymers as are particularly adapted for formulation of the spacer layer exhibit the property of being relatively soluble in cold water, that is, water at a temperature of less than about to 80 C., the precise temperature being dependent upon the polymer specifically selected for employment and relatively insoluble in hot water, that is, water at a temperature above about 80 C., the precise temperature being dependent upon the poly mer selected. A relatively large number of such polymers are substantially insoluble in a caustic photographic processing media over the range of photographic diffusion transfer processing. Such polymers, however, are permeable to photographic alkaline processing composition as a function of their swelling, which, in turn, is believed to be a function of the free energy of solution decrease caused, at least in part, by the heat evolved as a result of the interaction between the polymer and the processing composition solvent and by an increase of the entropy of the system. This free energy decrease is believed to lessen with increased temperature of the environment and result in a decreased swelling, and thus decrease photographic processing composition permeability with such temperature increase.

It has now been unexpectedly discovered that if the spacer layer of the last-identified copending application comprises cyanoethylated polyvinyl alcohol, vastly superior cold temperature processing performance, for example, processing -at a temperature in the order of about F. is achieved.

Specifically, as a preferred embodiment, employment of cyanoethylated polyvinyl alcohols which are temperature-inverting in the manner detailed above provides in a cold temperature processing environment higher transfer image maximum densities, increased photographic speed, increased flexibility of coating layer thickness p rameters, and, in multicolor photographic diffusion transfer processes, improved color isolation.

It will be evident from a consideration of the present invention that the polymeric spacer layer utilized herein may fall within an area on a permeation-time vs. temperature graph wherein the average slope of the line varies from slightly positive to slightly negative. A slope of zero would indicate that, at the ordinary processing range of approximately 40 F. to 100 F. the pH lowering mechanism would operate irrespective of the temperature. It must be emphasized that the precise temperatre-permeation characteristics of the spacer layer must be tailored to the photographic system selected as a whole and are dependent upon the relative dye diffusion constants and development times of the selected system which are required at various temperatures. In this respect determination of the constituents of suitable polymers for use as a spacer layer in a selected system is substantially empirical.

As indicated in the above-cited copending applications inverse temperature dependence of a polymeric film with regard to alkali permeability is not an unknown phenomenon, the use of this property having been disclosed for utilization in diffusion transfer photographic receiving sheets. Benefits are derived from using a temperatureinverting material in a process which depends upon permeation of liquids at a variety of temperatures, since, as the ambient temperature decreases, the polymer tends to form hydrates and swells thus facilitating permeation as a function of the degree of swell of the polymerdeswelling being inherent with an increase in temperature. It is well known that the diffusion rate of a liquid, for example, an alkali, will increase as the temperature increases. Since, in a typical diffusion transfer photographic process this rate is directly proportional to the progress of the transfer image formation per unit time, the benefit of devising a mechanism for controlling the diffusion rate inversely with temperature is recognized. The desired result is to have the temperature inverting material approximately counteract changes in diffusion rate of the permeating material with changes in temperature, Temperature inversion is, therefore, relative, since the precise properties desired would be dependent upon the response of the whole system to changes in temperature.

Extreme inverse temperature characteristics are generally not particularly desirable since the development of the photosensitive part of the system and the dye transfer are temperature dependent processes and should be functionally compatible with the temperature-permeation properties of the receiving sheet. An ideal spacer layer, therefore, should provide the system which it comprises with the proper dye permeation-temperature properties so that dye may diffuse from the photosensitive part of the system to the receiving sheet, as a function of development, in order to form a positive image in the receiving sheet within a predetermined time, irrespective of the processing temperature employed.

The temperature inverting characteristic of members of the class of polymers useful in the instant invention is probably attributable to the presence of a predetermined balance of hydrophobic groups to hydrophilic groups in the polymer molecule. The probable mechanism through which temperature inversion occurs is by the formation of hydrogen bonds between the hydrophilic portion of the polymer and the hydrogen of the solvent at low temperatures; the hydrogen bonding being discouraged as the temperature of the material is raised due to thermal destruction. The system thereupon takes the form of a less-hydrated, less-swollen, therefore less-permeable polymer as a function of the increase in temperature. It may then be said that the preferred polymers useful in the practice of the present invention are those which contain hydrophilic groups which cause swelling as a function of the solvatability of that group in a given solvent, and hydrophobic groups which modulate the swelling so that at some definite ratio of hydrophilic to hydrophobic groups, the resultant compound will have temperature-inverting properties. It may further be coneluded generally that the interactions responsible for temperature inversion are forces such as hydrogen-bonding and hydrophobic-hydrophobic bonding forces.

It has unexpectedly been found that cyanoethylated polyvinyl alcohol at various degrees of cyanoethylation, gives far better results when considering the above-mentioned criteria, and those to be discussed below, than other groups of polymers heretofore used for the instant purpose.

For purposes of the instant specification, references to percentages of cyanoethylation refers to the percentage of hydroxyl groups depending from the polyvinyl alcohol backbone which are converted to cyanoethyl ether groups.

In general it may be said that a completely hydrophilic material will not be temperature inverting. The addition of hydrophobic moieties to a polymer causes the solubility of the polymer-which is directly associated with the swellability of the polymerto decrease until the polymer is soluble, or swellable, as the case may be, only in cold water. As the hydrophobic content or, in this case, degree of cyanoethylation, is further increased, the polymer becomes insoluble but even coatings of such ma terials when applied from a solvent other than water may exhibit temperature inverse permeability to water.

As might be expected the thickness of the temperature inverting layer will be somewhat critical since the hydration mechanism of the layer actually forms holes in the film through which processing composition may fioW. In order to maintain uniformity in processing time, the thicknesses of the individual polymer layers utilized should be predetermined to achieve uniform permeation time throughout the operative temperature range. As a rule, thicknesses from 0.050.8 mil are the range in which desired processing times for permeation of the processing solution found in, for example, Polaroid Type 108 Land film packs, is achieved.

As stated above, the acid polymer layer utilized in a diffusion transfer receiving sheet is designed to decrease the hydrogen ion concentration of the processing composition and is at the same time a sink for salt residues which form in the top layer of the receiving sheet during the development process. If the processing temperature is too hot and no temperature inverting layer is used as a timing valve, poor dye densities and gappiness will be evident in the photograph. These phenomena are probably due to premature neutralization of the processing composition. When the temperature is cold and no temperature inverting timing layer is used, the neutralization of the devolping composition is too slow, which results in the maintenance of undesirable salts in the top layer of the photographic picture This manifests itself by way of dull, muddy colors and causes, in many instances, developing reagents to adhere to the top of the print rather than being selectively stripped away with the photosensitive sheet.

The present invention will be illustrated in greater detail in conjunction with the following specific example which sets out a representative photographic product and process which, however, is intended to be illustrative and not of limiting effect.

Example 1 An image-receiving element was prepared by coating a cellulose nitrate subcoated baryta paper with the partial butyl ester of polyethylene/maleic anhydride copolymer which may be prepared by refluxing, for 14 hours, 300 gms. of a DX-840-31 resin (trade name of Mensanto Chemical Co., St. Louis, Mo., for high viscosity polyethylene/maleic anhydride), 140 gms. of n-butyl alcohol and 1 cc. of 85% phosphoric acid' to provide a polymeric acid layer approximately 0.7 mil thick. The external surface of said acid layer was coated with a solution of a 62.5% substituted cyanoethylated polyvinyl alcohol to provide a polymeric spacer layer approximately 0.4 mil thick. The external surface of the spacer layer was then coated with a 2:1 mixture, by weight, of polyvinyl alcohol and poly-4-viny1 pyridine, at a coverage of approximately 600 mg./ft. to provide a polymeric imagereceiving layer approximately 0.30 mil thick. The thusprepared image-receiving element was then baked at 180 F. for 30 minutes and then allowed to cool.

The cyanoethylated polyvinyl alcohol was prepared as follows: In a round bottom three-necked flask 110.5 g. of polyvinyl alcohol is dissolved in a liter of water with stirring. The mixture was heated to 90 C. until complete solution was obtained. The solution is cooled to about 25 C. and 30 g. of 16.67% hydroxide and 265 g. of acrylonitrile are added with vigorous stirring. The mixture is allowed to stir at room temperature for 16 to 17 hours during which time the polymer precipitated out. 8 /2 g. of acetic acid is added to neutralize the sodium hydroxide and the mixture is stirred for about minutes. The mother liquor is decanted and the polymer is washed three or four times with warm water. The water is decanted and the polymer is then dissolved by adding about 200 ml. of p-dioxane and then precipitated by adding a liter of water. The mother liquor is again d'ecanted and the polymer is dissolved by adding about 500 ml. of dioxane. An analysis of the resulting polymer disclosed polyvinyl alcohol having 62.5% of its hydroxyl groups converted to cyanoethyl ether groups.

A multicolor, multilayer photosensitive element was prepared in a manner similar to that disclosed in the aforementioned copending U.S. application Ser. No. 565,135 and detailed hereinbefore. In general, the photosensitive elements comprised a support carrying a redsensitive silver halide emulsion stratum, a green-sensitive silver halide emulsion stratum and a blue-sensitive silver halide emulsion stratum. In turn, the emulsions had dispersed behind them in water-immiscible organic solvents and contained in separate gelatin polymeric layers, respectively, a cyan dye developer, a magenta dye developer and a yellow dye developer. A gelatin interlayer was positioned between the yellow dye developer layer and the green-sensitive emulsion stratum, and also between the magenta dye developer layer and the red-sensitive emulsion stratum. The particular dye developers employed in the photosensitive elements may comprise, for example, 1,4- bis (0c methyl B hydroquinonyl-ethylamino)-5,8- dihydroxyanthraquinone (a cyan dye developer); 2-(p- [2,5' dihydroxyphenethyl] phenylazo) 4 isopropoxy 1 naphthol (a magenta dye developer); and 1- phenyl 3 n hexyl carbamyl 4 (p-[hydroquinonylethyl] phenylazo) 5 pyrazolone (a yellow dye developer). The last-mentioned yellow and magenta dye developers are disclosed in U.S. Patent No. 3,134,764, issued May 26, 1964, and the cyan dye developer is disclosed in U.S. Patent No. 3,135,606, issued June 2, 1964. Multicolor photosensitive material of the tripack type employing dye developers may also be commercially procured from Polaroid Corporation, Cambridge, Mass., as such material comprises the negative component of the photographic film distributed by that corporation under the trade designation of Polacolor Type 108 Land film.

The photosensitive element was then exposed and processed at various temperatures by spreading an aqueous liquid processing composition at a pH of not less than about 12 which comprised:

Water cc Potassium hydroxide gms 11.2 Hydroxyethyl cellulose (high viscosity) [commercially available from Hercules Powder Co., Wilmington, Del., under the trade name Natrasol 250] gms 4.03 Potassium thiosulfate gm 0.5 Benzotriazole gms 3.5 N-benzyl-a-picolinium bromide gms 2.3 Lithium hydroxide gm 0.3

between said image-receiving element and said exposed multicolor element as they were brought into superposed relationship in a Polaroid Land pack camera. After an imbibition of 60 seconds or seconds, for tests carried out at 75 and 100 F. or 50 F., respectively, the pH of the processing composition having been reduced below about 8, the image-receiving element was separated from the remainder of the film assembly.

Quantalog MacBeth Densitometer.

ADmBX 62.5% substituted ADM! Polyvinyl alcohol cyanoethylated polyvinyl control spacer layer Temperaalcohol spacer layer ture, F.

Red Green Blue Red Green Blue It is evident that vastly superior results are obtainable using the polymers of the instant invention as a spacer layer in a receiving sheet.

Example 2 ADM, 47% substituted cy- ADmX polyvinyl alcohol anoethylated polyvinyl control spacer layer Temperaalcohol spacer layer ture, F.

Red Green Blue Red Green Blue Although the preferred image-receiving layer is a mixture of polyvinyl alcohol and poly-4-vinylpyridine, the invention is not limited thereto. Other image-receiving layers are known in the art and may be employed. Similarly, while the preferred embodiment effects development in the presence of a quaternary ammonium compound (as disclosed and claimed in US. Patent No. 3,173,786, issued on Mar. 3, 1965) and particularly, a quaternary ammonium compound capable of forming an active methylene base in alkali, the invention is not so limited, even though the advantages are most dramatic when such an active methylene quaternary ammonium salt is used.

The support layers referred to may comprise any of the various types of conventional rigid or flexible supports, for example, glass, paper, metal, and polymeric films of both synthetic types and those derived from naturally occurring products. Suitable materials include paper; aluminums; polymethacrylic acid, methyl and ethyl esters; vinyl chloride polymers; polyvinyl acetal; polyamides such as nylon; polyesters such as polymeric films derived from ethylene glycolterephthalic acid; and cellulose derivatives such as cellulose acetate, triacetate, nitrate, propionate, butyrate, acetate-propionate, or acetatebutyrate,

Where desired, the support for the image-receiving layer may be transparent or opaque. Suitable opacifying agents may be incorporated in the negative and/or positive to permit imbibition to be completed outside of a camera, i.e., in an area exposed to light actinic to the silver halide emulsions.

Use of the novel image-receiving elements of this invention makes feasible the use, over an extended range of ambient temperature, of image dyes which are pH sensitive, and particularly the use of dye deevlopers having less pH insulation since the final pH of the image layer can be more accurately and reproducibly controlled.

Processing preferably is effected in the presence of an auxiliary or accelerating silver halide developing agent which is substantially colorless, at least in the unoxidized form. Particularly useful are substituted hydroquinones, such as phenylhydroquinone, 4-methylphenylhydroquinone, toluhydroquinone, tertiarybutylhydroquinone, and 2,5-triptycene diol. These hydroquinones may be employed as components of the processing composition or they may be incorporated in one or more layers of the negative. Particularly useful results are obtained when 4 -methylphenylhydroquinone is dispersed in one or more of the gelatin interlayers and/ or in a gelatin layer coated over the blue-sensitive emulsion layer.

As noted above, this invention contemplates reduction of the positive image pH to a level substantially precluding aerial oxidation of developer moieties. The provision of antioxidants, such as arbutin, prior to exposure of the image to air to provide additional protection against oxidation also is within the scope of this invention. Since the reduction in pH continues for at least a short time after the positive image is separated from the negative, provision of such an anti-oxidant permits the positive to be separated at a slightly higher pH than would be otherwise desirable.

It is also contemplated to provide other adjuvants, e.g., ultraviolet absorbers, effective to improve the light stability or other properties of the positive image. Thus, an ultraviolet absorber may be included in the processing composition and deposited on the image-receiving layer during imbibition, or it may be present in a thin overcoat on the image-receiving layer prior to imbibition.

In all preferred embodiments of this invention the polymeric acid layer preferably is thicker than the imagereceiving layer and has an appreciably higher mg./ft. coverage. The image-receiving layer is preferably about 0.25 to 0.4 mil thick, the polymeric acid layer is preferably 0.3 to 1.5 mil thick, and the described spacer layer is preferably about 0.05 to 0.8 mil thick.

Although the invention has been illustrated in connection with dye developers, and the invention is particularly applicable to dye developers because of their susceptibility to aerial oxidation at high pH, the novel imagereceiving elements of this invention may be used in other diffusion transfer processes such as those previously described to obtain pH reduction and particularly to obtain transfer images exhibiting great optical clarity and luminosity over an extended range of ambient temperatures.

In addition to the described essential layers, it will be recognized that the image-receiving elements may also contain one or more additives such as plasticizers, intermediate essential layers for the purpose, for example, of improving adhesion, etc.

Since certain changes may be made in the above products and processes without departing from the scope of the invention herein involved, it is intended that all matter contained in the above description shall be interpreted as illustrative and not in a limiting sense.

What is claimed is:

1. A receiving sheet for use in a photographic diffusion transfer process comprising a composite sheet material comprising a plurality of essential layers including in sequence a support; a polymeric acid layer; a layer comprising cyanoethylated polyvinyl alcohol; and an alkalipermeable and dyeable polymeric layer.

2. The invention of claim 1 wherein cyanoethylated polyvinyl alcohol contains cyanoethyl moieties to a degree which provides the polymer with predetermined temperature-alkali permeable characteristics.

3. The invention of claim 1 wherein the said cyanoethylated polyvinyl alcohol is substituted from about 47 to 62.5% with cyanoethyl moieties.

4. The invention of claim 2 wherein said cyanoethylated polyvinyl alcohol is characterized by decreasing al kali solution permeability with increasing temperature.

5. A process for forming a diffusion transfer color image which comprises the steps of developing an exposed photosensitive element comprising a plurality of layers including a silver halide emulsion layer, at least one of said layers containing a dye, which dye is a silver halide developing agent, by contacting said element with an aqueous alkaline processing solution, immobilizing said dye in the exposed areas of said element as a result of development, forming thereby an imagewise distribution of mobile dye as a function of the point-to-point degree of exposure of said element, transferring by imbi-bition at least a portion of said imagewise distribution of mobile dye to a superposed image-receptive element which comprises a plurality of layers including, in sequence, a support layer; a polymeric acid layer; a permeable polymeric layer comprising cyanoethylated polyvinyl alcohol; and a solution dyeable and permeable polymeric layer to provide to said dyeable polymeric layer a dye image; transferring by imbibition subsequent to substantial positive image formation at least a portion of the ions of said alkaline solution through each of said permeable polymeric layers to said polymeric acid layer to thereby reduce the alkalinity of the processing solution.

6. The invention of claim wherein said cyanoethylated polyvinyl alcohol contains cyanoethyl moieties to a degree which provides the polymer with predetermined temperature-alkali permeable characteristics.

7. The invention of claim 6 wherein said cyanoethylated polyvinyl alcohol is substituted from about 47 to 62.5% with cyano ethyl moieties.

8. The invention of claim 6 wherein said cyanoethylated polyvinyl alcohol is characterized by decreasing alkali solution permeability with increasing temperature.

9. In a multicolor diffusion transfer process which comprises the steps of developing an exposed photosensitive element comprising a plurality of layers including blue-sensitive, green-sensitive and red-sensitive silver halide gelatin emulsion layers mounted on a common support, said blue-sensitive, green-sensitive and red-sensitive silver halide emulsion layers being contiguous to yellow, magenta and cyan dyes, respectively, each of said dyes being silver halide developing agents, by permeating said photosensitive element with an aqueous alkaline processing composition having an initial pH of not less than about 12; immobilizing said yellow, magenta and cyan dyes as a result of development; forming thereby an imagewise distribution of mobile yellow, magenta and cyan dye, as a function of the point-to-point degree of exposure of said element, transferring, by imbibition, at least a portion of each of said imagewise distributions of mobile dye to a superposed image-receiving element comprising a plurality of essential layers including, in sequence, a support layer; a polymeric alkali acceptor layer;

a permeable polymeric layer comprising a cyanoethylated polyvinyl alcohol; and an alkaline solution dyeable and permeable polymeric layer; to provide to said dyeable polymeric layer a multicolor dye image; transferring, by imbibition, subsequent to substantial transfer image formation, at least a sufiicient portion of the alkali of said processing composition through each of said permeable polymeric layers to said polymeric alkali acceptor layer to provide thereby a reduction of the pH of said composition and then separating said image-receiving element from said superposed relationship.

10. The invention of claim 9 wherein said cyanoethylated polyvinyl alcohol contains cyanoethyl moieties to a degree which provides the polymer with predetermined References Cited UNITED STATES PATENTS 3,325,283 6/1967 Barstow et al 963 3,345,165 10/1968 Land 9629 NORMAN G. TORCHIN, Primary Examiner.

A. T. SURO-PICO, Assistant Examiner.

US. Cl. X.R. 9629 

9. IN A MULTICOLOR DIFFUSION TRANSFER PROCESS WHICH COMPRISES THE STEPS OF DEVELOPING AN EXPOSED PHOTOSENSITIVE ELEMENT COMPRISING A PLURALITY OF LAYERS INCLUDING BLUE-SENSITIVE, GREEN-SENSITIVE AND RED-SENSITIVE SILVER HALIDE GELATIN EMULSION LAYERS MOUNTED ON A COMMON SUPPORT, SAID BLUE-SENSITIVE, GREEN-SENSITIVE AND RED-SENSITIVE SILVER HALIDE EMULSION LAYERS BEING COMTIGUOUS TO YELLOW, MAGENTA AND CYAN DYES, RESPECTIVELY, EACH OF SAID DYES BEING SILVER HALID DEVELOPING AGENTS, BY PERMEATING SAID PHOTOSENSITIVE ELEMENT WITH AN AQUEOUS ALKALINE PROCESSING COMPOSITION HAVING AN INTIAL PH OF NOT LESS THAN ABOUT 12; IMMOBILIZING SAID YELLOW, MAGENTA AND CYAN DYES AS A RESULT OF DEVELOPMENT; FORMING THEREBY AN IMAGEWISE DISTRIBUTION OF MOBILE YELLOW, MAGENTA AND CYAN DYE, AS A FUNCTION OF THE POINT-TO-POINT DEGREE OF EXPOSURE OF SAID ELEMENT, TRANSFERRING, BY IMBIBITION, AT LEAST A PORTION OF EACH OF SAID IMAGEWISE DISTRIBUTIONS OF MOBILE DYE TO A SUPERPOSED IMAGE-RECEIVING ELEMENT COMPRISING A PLURALITY OF ESSENTIAL LAYERS INCLUDING, IN SEQUENCE, A SUPPORT LAYER; A POLYMERIC ALKALI ACCEPTOR LAYER; A PERMEABLE POLYMERIC LAYER COMPRISING A CYANOETHYLATED POLYVINYL ALCOHOL; AND AN ALKALINE SOLUTION DYEABLE AND PERMEABLE POLYMERIC LAYER; TO PROVIDE TO SAID DYEABLE POLYMERIC LAYER A MULTICOLOR DYE IMAGE; TRANSFERRING, BY IMBIBITION, SUBSEQUENT TO SUBSTANTIAL TRANSFER IMAGE FOR MATION, AT LEAST A SUFFICIENT PORTION OF THE ALKALI OF SAID PROCESSING COMPOSITION THROUGH EACH OF SAID PERMEABLE POLYMERIC LAYERS TO SAID POLYMERIC ALKALI ACCEPTOR LAYER TO PROVIDE THEREBY A REDUCTION OF THE PH OF SAID COMPOSITION AND THEN SEPARATING SAID IMAGE-RECEIVING ELEMENT FROM SAID SUPERPOSED RELATIONSHIP. 